1. Field of the invention
The invention relates to apparatus for optically checking the profile of the inner wall of a tube or bore.
The apparatus is particularly suitable for the in situ inspection of the tubes of steam generators in nuclear power stations, which must be inspected regularly to detect any defects which may lead to them cracking under stress, but may be used for the inspection of any tubes or bores of great length and small diameter, whether straight or having bends.
2. Summary of the prior art
The inspection of such tubes may be carried out by a technique which makes use of Foucault currents for the detection of defects in the tube walls. This method is described in French Pat. No. 2 320 542. It may also be carried out by measuring the internal profile of the tube, and the present invention falls within this latter category.
One known technique of determining the internal profile of a tube involves using a multi-fingered probe for the simultaneous measurement of the internal radius of the tube at various positions around the circumference, when the probe is pulled along the tube, by detecting the deflection of strain gauges mounted on the fingers. Such a device is described, for example, in French Pat. No. 2 553 877.
Another known technique, described for example in French Pat. No. 2 513 753, makes use of a profile probe having a motor driven rotary head rotating about a longitudinal axis of the probe. A measuring element carried by the head makes contact with the inner surface of the tube wall.
These known devices are restricted in their field of use by the contact required between the measuring element and the inner wall, as well as by the associated mechanical devices making their miniaturization difficult, or even impossible, sufficient for them to be used in the curved areas of steam generator tubes.